XMR angle sensors

ABSTRACT

Embodiments relate to xMR sensors, sensor elements and structures, and methods. In an embodiment, a sensor element comprises a non-elongated xMR structure; and a plurality of contact regions formed on the xMR structure spaced apart from one another such that a non-homogeneous current direction and current density distribution are induced in the xMR structure when a voltage is applied between the plurality of contact regions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/950,456 filed on Nov. 19, 2010, which is a continuation-in-part ofU.S. application Ser. No. 11/941,853 filed on Nov. 16, 2007, thecontents of which are incorporated by reference in their entirety.

FIELD

The invention relates generally to integrated circuit (IC) sensors andmore particularly to magnetoresistive IC angle sensors.

BACKGROUND

Magnetoresistive sensors can include anisotropic magnetoresistive (AMR),giant magnetoresistive (GMR), tunnel magnetoresistive (TMR) and othertechnologies, referred to collectively as xMR technologies. XMR sensorscan be used for a variety of applications, including magnetic field andcurrent sensors, speed sensors, rotation sensors and angle sensors,among others.

The accuracy of AMR angle sensors is limited by magnetic anisotropy andhysteresis effects. Key influencing factors are magnetic domains nearthe structure edge because the shape anisotropy caused by thedemagnetizing field is strongest near the edge. Furthermore, defects atthe edge related to the etch process can act as pinning centers thatpotentially lead to domain generation responsible for hysteresiseffects. While shape anisotropy can be reduced by using wider AMRstripes, this requires bigger chip size as well as a larger signal fieldmagnet.

In GMR and TMR angle sensors, however, AMR effects are parasitic andundesirable. TMR structures typically require a top contact and a bottomcontact to induce a current perpendicular to the sensor plane. If a TMRcurrent-in-plane (CIP-TMR) concept is used, the same structures as forGMR sensors can be used, obtaining a higher sensor signal. The mainreasons for angle error remaining after full compensation are magneticanisotropy effects and, as previously mentioned, AMR effects, which areconsidered parasitic. AMR effects can be suppressed by using shapedmeanders having orthogonal strip length axes. In order to reduce anyremaining anisotropy effect, the strip width can be made wider, therebyincreasing the chip size, which is undesirable and increases cost.

Therefore, a need remains for an improved xMR sensor.

SUMMARY

Embodiments relate to xMR sensors, sensor elements and structures, andmethods. In an embodiment, a sensor element comprises a non-elongatedxMR structure; and a plurality of contact regions formed on the xMRstructure spaced apart from one another such that a non-homogeneouscurrent direction and current density distribution are induced in thexMR structure when a voltage is applied between the plurality of contactregions.

In an embodiment, a sensor comprises a first non-elongated xMR elementhaving a plurality of contact regions formed on the first xMR elementspaced apart from one another such that a locally non-homogenous currentdirection and current density distribution are induced in the first xMRelement when a voltage is applied between the plurality of contactregions and a net current direction in the first xMR element defines afirst axis; and a second non-elongated xMR element having a plurality ofcontact regions formed on the second xMR element spaced apart from oneanother such that a locally non-homogenous current direction and currentdensity distribution are induced in the second xMR element when avoltage is applied between the plurality of contact regions and a netcurrent direction in the second xMR element defines a second axis, thesecond axis being substantially orthogonal with respect to the firstaxis.

In an embodiment, a sensor element comprises a non-elongated xMRelement; a first contact region formed on the xMR element and coupled toa first terminal; a second contact region formed on the xMR element andcoupled to a second terminal and spaced apart from the first contactregion along a first contact axis; and a third contact region formed onthe xMR element and coupled to the second terminal and spaced apart fromthe first contact region along a second contact axis rotated ninetydegrees with respect to the first contact axis.

In an embodiment, a method comprises forming an xMR sensor element;forming a plurality of contact regions on the xMR sensor element spacedapart from one another and proximate an edge of the xMR sensor element;and causing a current to flow in the xMR sensor element with a locallynon-homogenous current direction and current density distribution.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a block diagram of an xMR structure according to anembodiment.

FIG. 2 is a diagram of an xMR structure according to an embodiment.

FIG. 3 is a diagram of simulated current direction distributionaccording to the embodiment of FIG. 2.

FIG. 4 is a diagram of simulated current density distribution accordingto the embodiment of FIG. 2.

FIG. 5 is a distribution histogram of current angles with respect to thevertical axis for the 0-90 degree quadrant for the embodiment of FIG. 2.

FIG. 6A is a diagram of an xMR structure according to an embodiment.

FIG. 6B is a diagram of an xMR structure according to an embodiment.

FIG. 6C is a diagram of an xMR structure according to an embodiment.

FIG. 7 is a diagram of simulated current direction distributionaccording to the embodiment of FIG. 6.

FIG. 8 is a diagram of simulated current density distribution accordingto the embodiment of FIG. 6.

FIG. 9 is a distribution histogram of current angles with respect to thevertical axis for the 0-90 degree quadrant for the embodiment of FIG. 6.

FIG. 10 is a diagram of an xMR structure according to an embodiment.

FIG. 11 is a diagram of simulated current direction distributionaccording to the embodiment of FIG. 10.

FIG. 12 is a diagram of simulated current density distribution accordingto the embodiment of FIG. 10.

FIG. 13 is a distribution histogram of current angles with respect tothe vertical axis for the 0-90 degree quadrant for the embodiment ofFIG. 10.

FIG. 14 is a diagram of an xMR structure according to an embodiment.

FIG. 15 is a diagram of simulated current density distribution accordingto an embodiment.

FIG. 16 is a diagram of an xMR structure according to an embodiment.

FIG. 17 is a diagram of an xMR structure according to an embodiment.

FIG. 18 is a diagram of simulated current direction distributionaccording to the embodiment of FIG. 17.

FIG. 19 is a diagram of simulated current density distribution accordingto the embodiment of FIG. 17.

FIG. 20 is a diagram of an xMR structure according to an embodiment.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Embodiments relate to xMR sensors having xMR structures with very lowshape anisotropy effects. The xMR structures can comprise anisotropicmagnetoresistive (AMR), giant magnetoresistive (GMR) or tunnelmagnetoresistive (TMR) technologies. In embodiments, the xMR structurescan be shaped such that they present orthogonal net current directions,for example being round. In other embodiments, the xMR structures can besquare, oval, slightly rectangular, octagonal, hexagonal or have someother multi-sided configuration. In general, the xMR structures arenon-elongated, having a width or first lateral dimension that is notsignificantly greater or less than a length or second lateral dimensiontaken at approximately ninety degrees from the first lateral dimension,or wherein a ratio of the first dimension to the second dimension isless than about 1.5 in embodiments. Embodiments also comprise pointcurrent contacts, strip current contacts or other contact and contactregion structures configured to obtain a distribution of positive andnegative angles with respect to the net current.

Embodiments thereby enable harmonic filtering effects to be utilized.Furthermore, the current density in embodiments is not homogeneous andis reduced in magnetically disadvantageous edge regions. Moreover,because of the contact design in embodiments the current distributioncan be modified to achieve a variation of the angle distribution of thecurrent directions and therefore to vary and tailor the harmonicfiltering effect. In addition, the square resistance is significantlyenhanced compared to a structure with homogeneous current distributionover the full structure width, thereby reducing the power consumption atthe same sensor size.

Different contact designs can affect the distributions of current anglesand current densities. When considering tailoring the contact design, aconcept for a monolithic integration of AMR structures, such as isdisclosed in commonly owned DE 10 2005 047482 A1 which is incorporatedherein by reference in its entirety, can be considered. Referring toFIG. 1, contact between xMR portion, here depicted as GMR, to the wiringmetal is made by conductive vias beneath an AMR structure. Because thevia size can be as small as 0.4 micrometers (μm) by 0.4 μm inembodiments or can be of larger sizes, such as long vias or stripcontacts, a variety of different contact designs is possible. Further,conductive vias can also be used to form highly conductive (as comparedto the AMR material) regions to influence current distribution. Inembodiments discussed in more detail below, contact regions comprisemetal and/or are at least partially metallic.

Therefore, and referring to FIG. 2, an embodiment of a circular xMRelement or structure 202 is depicted, such as AMR in the embodiment ofFIG. 2, in combination with point contact regions 204. Point contactregions 204 can be located proximate though spaced apart from an edge ofxMR structure 202. In embodiments, point contact regions 204 cancomprise vias to couple xMR structure 202 to an underlying wiring metalor other structure.

In one embodiment, a diameter of xMR structure 202 is about 14 μm and adiameter of contact regions 204 is about 1 μm or less, though these andother dimensions can vary in other embodiments. For example, a diameterof xMR structure 202 can vary from about 1 μm to about 100 μm or more inembodiments, such as about 5 μm to about 20 μm in embodiments. While xMRstructure 202 is essentially round in the embodiment of FIG. 2, theshape can vary in other embodiments and can be, for example, oblong ormultisided, such as a hexagon, octagon, square or some other shape.

When a voltage is applied to contact regions 204, current directionsvary locally. FIG. 3 depicts, for an embodiment of xMR structure 202,simulated local distribution of resulting current directions withrespect to the vertical axis which is defined by the voltage gradient.FIG. 3 illustrates how the current direction distribution in structure202 can be changed by tailoring the contact regions 204 as opposed toconventional attempts which altered the geometry of the xMR structureitself.

The AMR effect is proportional to sin(α)², with a being the anglebetween the magnetization and the current direction. Therefore, positiveand negative angles with respect to the vertical axis are equivalent, asare the upper and lower half-spaces. Thus, only angles between 0 andninety degrees are considered. In the example simulation depicted, themain current direction is along the vertical 0-degree axis, with anotherportion distributed between 0 degrees and forty-five degrees. In someregions near contacts 204 more horizontal directions with angles greaterthan forty-five degrees can be seen (refer, for example, to FIG. 5). InFIG. 3, the mean current direction without being weighted with the localcurrent density is calculated to be about +/−22 degrees with respect tothe vertical orientation.

FIG. 4 depicts simulated current density distribution for xMR structure202. Due to the limited size of contact regions 204, the current densityis not homogenous over xMR structure 202. As can be seen in FIG. 4, theleft and right edges of xMR structure 202 exhibit lower current densitycompared with the central region. As a result, the edge regions, whichare critical for magnetic performance, do not contribute fully to theelectrical sensor signal, thereby reducing the angle error. Theinfluence of the distribution of the current directions on the AMRoutput signal can be calculated by weighting the sin(α)² with the localcurrent density. According to the numerical simulations, the AMR signalis expected to be about 47% lower compared with the case of ahomogeneous current distribution. On the other hand, the resistance isincreased by 92% in an embodiment. By comparison, in a strip structureembodiment with a homogenous current distribution this could only beachieved by an approximate halving of the strip width which would inturn relate to a significant increase in angle error. In FIG. 4, theresistance is about 1.9 squares. A corresponding distribution histogramis depicted in FIG. 5.

Another embodiment of an xMR structure or element 602 is depicted inFIG. 6A. XMR structure 602 comprises two long, strip-like via contacts604. As can be seen in FIG. 7, the simulated current directions in theembodiment of FIG. 6A are more aligned along the vertical axis, whichcan also be seen in a much narrower current direction distribution inFIG. 8, resulting in an average current angle with respect to thevertical axis of about +/−11 degrees. A corresponding distributionhistogram is depicted in FIG. 9.

In the embodiment of FIG. 6A, the AMR signal is expected to be about 14%lower compared with the case of homogeneous current distribution. On theother hand, the resistance is about 20% higher in an embodiment.

Other embodiments are depicted in FIGS. 6B and 6C, in which xMRstructure 602 is at least somewhat analogous to the embodiment FIG. 6A.In FIG. 6B, xMR structure 602 comprises two strip-like contacts 604 eachcomprising a plurality of spaced apart single vias 605. For redundancy,such as to ensure sensor functionality in the case that a particular via605 loses its contact by, e.g., delamination, vias 605 can be positionedin a second line or array as depicted in FIG. 6C. Vias 605 generally donot influence the current distribution in xMR structure 602 as long asvias 605 in at least one line exhibit a suitable contact 604 for xMRstructure 602. The number, placement and configuration of contacts 604and vias 605 can vary in other embodiments, for example by comprisingmore or fewer vias 605 or in other arrangements with respect to eachother and xMR structure 602 than as depicted in FIG. 6. Further, otherembodiments depicted and discussed elsewhere herein can also comprisecontacts having pluralities of vias.

The xMR structures 202 and 602 of FIGS. 2 and 6, respectively,demonstrate how different contact designs can influence the currentdistribution and therefore the effect on the harmonic filtering effectas well as the specific resistance. Other embodiments not specificallydepicted include varying circular or multi-sided xMR structureconfigurations in combination with varying point, strip and othercontact and contact region configurations. The ability to vary theconfigurations and/or combinations gives rise to numerous advantages inembodiments. For example, advantages of circular or multi-sided AMRstructures as disclosed herein can include low shape anisotropy withlower angle error and lower hysteresis; when combined with varyingcontact designs, advantages can further include adjustable currentdirection distribution and adjustable harmonic filtering effects as wellas adjustable current density distribution, further reduced shapeanisotropy effects, further reduced hysteresis effects and increasedspecific resistance.

Another embodiment is depicted in FIG. 10 in which an xMR structure orelement 1002 comprises another contact design. Each contact region 1004comprises a point contact 1006 and two adjacent conducting andelectrically isolated strip structures 1008. Strip structures 1008 aregenerally highly conductive, with conductivity depending upon thegeometric size and, in embodiments, being from about five times to aboutfifty times higher compared with the AMR/GMR sheet resistance. Stripstructures 1008 are not directly coupled to a voltage in an embodiment.Because of the higher conductivity of strip structures 1008 compared tothe AMR material of xMR structure 1002, the electric field distributionis varied, resulting in a current direction distribution similar to thestrip contact embodiment depicted in FIG. 6. In the embodiment of FIG.10 and also referring to FIG. 11, the average current direction is about+/−17 degrees, resulting in an AMR signal expected to be about 32% lowerand a specific resistance which is about 62% higher compared to the caseof a homogeneous current distribution. FIG. 12 depicts simulated currentdensity distribution for xMR structure 1002, while FIG. 13 is ahistogram of current angle distribution with respect to the verticalaxis.

In an embodiment, a plurality of xMR structures or elements are coupledserially, such as is depicted in FIG. 14. Such a configuration can beimplemented if an extension of the current direction distribution isdesired or required. In the embodiment of FIG. 14, the serial couplingof a plurality of xMR structures 1402 can provide varying tilt angles ofthe vertical axis, or voltage gradient, such that a desired axis can beobtained. For effective harmonic filtering, the tilt angles are pairedequally positive and negative. In other words, a first angle, −φ, isformed between the voltage gradient axis of structure 1402 b and thedesired axis, and a second angle, +φ, is formed between the voltagegradient axis of structure 1402 c and the desired axis, the first andsecond angles being equal but having opposing signs. In an embodiment,the contacts 1404 of adjacent xMR structures 1402 are coupled by metalconnectors 1406, though the size, shape, configuration and orientationof the connectors 1406 can vary in embodiments from as depicted in theembodiment of FIG. 14.

As previously mentioned, the AMR effect desired in AMR embodiments isparasitic in GMR and TMR embodiments. Therefore, in these and perhapsother embodiments it is desired to suppress the AMR effect. Inembodiments, this can be accomplished at least in part by implementingcircular or multi-sided GMR and TMR structures, such as discussed hereinabove, in combination with an orthogonal current feed. This provides astructure with a minimum shape anisotropy, e.g. round, and therefore aminimum angle error. Because the sensor layer often comprises an NiFealloy, the AMR effect in GMR and TMR devices contributes to theremaining angle error. A combination of GMR/TMR elements exhibitingorthogonal current directions will lead to cancelation of theAMR-induced resistance change and, therefore, to a suppression of theAMR effect influence on angle accuracy in embodiments.

An embodiment of a GMR or TMR device is very similar or identical to thedevice of FIG. 2 except that xMR structure 202 comprises a GMR or TMRstructure or element. According to simulations of embodiments, the pointcontact design of contacts 204 results in a non-homogenous currentdistribution: most of the carriers flow in the middle region of GMR/TMRstructure 202, which is favorable with respect to an output signal oflow anisotropy error since the edge regions exhibit a disadvantageousmagnetic behavior. A significant advantage of the configuration of pointcontacts 204 in embodiments is an enhanced specific resistance, such asalmost a doubling in an embodiment, which enables a reduction of theactive GMR/TMR area at a certain total resistance. Simulated currentdensity is depicted in FIG. 15.

To suppress a resistance modulation due to AMR effects in GMR/TMRembodiments, an equal number of elements orthogonally oriented withrespect to each other and the voltage gradient axis, a plurality ofGMR/TMR structures can be serially coupled, such as is depicted in FIG.16. FIG. 16 depicts a plurality of GMR/TMR structures 1602, eachcomprising point contacts 1604, coupled by connectors 1606. In anembodiment, connectors 1606 comprise metal connectors.

Another embodiment is depicted in FIG. 17. In FIG. 17, a GMR/TMRstructure or element 1702 comprises a plurality of point contacts 1704.The three contacts 1704 are arranged such that one is generallypositioned in the center of GMR/TMR structure 1702, coupled to a firstterminal, and two are located near the edge defining an angle of 90degrees and coupled to a second terminal. As a result, element 1700exhibits two parallel current paths which are orthogonal to each other,such as can be seen in the simulation results of FIG. 18. Simulatedcurrent density is depicted in FIG. 19. Although the specific resistancedecreases, it is still about 0.7 squares in an embodiment, which iswithin a reasonable range. An advantage of the embodiment of FIG. 17 isthat AMR effect-based resistance modulation is suppressed in a singleelement.

Another multi-element embodiment is depicted in FIG. 20. Here, GMR/TMRstructures 2002 remain coupled by GMR/TMR bridges 2006 with underlyingvias 2010. In embodiments, bridges 2006 have widths in a range of about0.1 μm to about 10 μm, such as about 0.5 μm to about 2 μm, and lengthsin a range of about 0.1 μm to about 10 μm, such as about 0.5 μm to about2 μm. In other embodiments, more or fewer GMR/TMR structures 2002 can becoupled, and the structures 2002 can be coupled in alternateconfigurations, keeping in mind that an equal number of elementsorthogonally oriented with respect to each other and the voltagegradient axis is desired. In another embodiment, alternate contactconfigurations are used for a shortening of the GMR/TMR bridge 2006configuration, such as single via contacts in combination with a wiringmetal as depicted in FIG. 14.

Another embodiment comprises an AMR element according to FIG. 16, FIG.17 or FIG. 20. In some applications, it can be necessary to provide AMRresistors with certain temperature coefficients of resistance withoutexhibiting a magnetoresistive effect when an external magnetic field isapplied. For example, a Wheatstone half-bridge can be realized with suchan element.

Various embodiments of xMR sensor structures, including AMR, GMR and/orTMR, have been discussed herein. These structures can have variousconfigurations in embodiments, including round or multi-sided, and arecombined with contacts and contact regions having various arrangementsand configurations, including point, strip, multi-portioned and others.Embodiments are not limited to those specifically depicted or discussed,as various other combinations, configurations and arrangements can beformed, as understood by those skilled in the art. As discussed,embodiments having varying and various contact and contact regionconfigurations enable alteration of the current direction distributionin the underlying xMR structure, as compared with conventionalapproaches which altered the geometry of the xMR structure itself.

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the invention. It should be appreciated,moreover, that the various features of the embodiments that have beendescribed as well as of the claims may be combined in various ways toproduce numerous additional embodiments. Moreover, while variousmaterials, dimensions, shapes, implantation locations, etc. have beendescribed for use with disclosed embodiments, others besides thosedisclosed may be utilized without exceeding the scope of the invention.

Persons of ordinary skill in the relevant arts will recognize that theinvention may comprise fewer features than illustrated in any individualembodiment described above. The embodiments described herein are notmeant to be an exhaustive presentation of the ways in which the variousfeatures of the invention may be combined. Accordingly, the embodimentsare not mutually exclusive combinations of features; rather, theinvention may comprise a combination of different individual featuresselected from different individual embodiments and/or from differentclaims, as understood by persons of ordinary skill in the art.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the present invention, it isexpressly intended that the provisions of Section 112, sixth paragraphof 35 U.S.C. are not to be invoked unless the specific terms “means for”or “step for” are recited in a claim.

What is claimed is:
 1. A sensor element comprising: a plurality ofnon-elongated xMR structures being serially coupled; and at least aselected one of the plurality of non-elongated xMR structurescomprising: a first contract region and a second contact region formedon the xMR structure and spaced apart from one another such that anon-homogeneous current direction and current density distribution areinduced in the selected xMR structure when a voltage is applied betweenthe first and second contact regions.
 2. The sensor element of claim 1,wherein the first and second contact regions are each proximate an edgeof the selected one of the plurality of non-elongated xMR structures. 3.The sensor element of claim 1, wherein a first axis is defined in adirection of a maximum lateral dimension of the selected one of theplurality of non-elongated xMR structures and a second axis is definedsubstantially perpendicular to the first axis, wherein a ratio ofdimensions of the xMR structure along the first and second axes is lessthan about 1.5.
 4. The sensor element of claim 1, wherein the selectedone of the plurality of non-elongated xMR structures has equal lateraldimensions.
 5. The sensor element of claim 1, wherein the selected oneof the plurality of non-elongated xMR structures is rotationallysymmetrical.
 6. The sensor element of claim 1, wherein the selected oneof the plurality of non-elongated xMR structures is of a polygonalshape, and is of rotational symmetry.
 7. The sensor element of claim 1,wherein the selected one of the plurality of non-elongated xMRstructures has a radius.
 8. The sensor element of claim 7, wherein theselected one of the plurality of non-elongated xMR structures issubstantially round.
 9. The sensor element of claim 1, furthercomprising at least one highly conductive region disposed adjacent atleast one of the plurality of contact regions.
 10. A sensor elementcomprising: a non-elongated xMR element; a first contact region formedon the xMR element and coupled to a first terminal; a second contactregion formed on the xMR element and coupled to a second terminal andspaced apart from the first contact region along a first contact axis;and a third contact region formed on the xMR element and coupled to thesecond terminal and spaced apart from the first contact region along asecond contact axis rotated ninety degrees with respect to the firstcontact axis such that two electrically parallel current paths, whichare physically orthogonal to one another, are exhibited by the xMRelement.
 11. The sensor element of claim 10, wherein the first contactregion is disposed in the approximate center of the xMR element and thesecond and third contact regions are disposed proximate an edge of thexMR element, the second and third contact regions spaced apart from oneanother.
 12. A method comprising: forming an xMR sensor element;forming: a first contact region on the xMR element and coupled to afirst terminal; a second contact region on the xMR element and coupledto a second terminal and spaced apart from the first contact regionalong a first contact axis; and a third contact region on the xMRelement and coupled to the second terminal and spaced apart from thefirst contact region along a second contact axis rotated ninety degreeswith respect to the first contact axis such that two electricallyparallel current paths, which are physically orthogonal to one another,are exhibited by the xMR element; and causing a current to flow in thexMR sensor element with a locally non-homogenous current direction andcurrent density distribution.